In the context of the EST design study for a 4m-class solar telescope and a study for large open-foldable domes of the
Dutch Technology Foundation STW, a design is made for the 20 to 30m diameter range. Detailed designs are made for
three specific diameter sizes: 23, 28 and 33m. Smaller-size open-foldable domes based on tensioned cloth and in use at
the Dutch Open Telescope (7m) and the GREGOR (9m) have proven to be all-weather stable and very effective for good
seeing conditions for solar telescopes. The cloth has shown no degradation over the past 14 (DOT) resp. 6 (GREGOR)
years of experience and no permanent elongation with the frequent de-tensioning and tensioning during opening and
closing. The application of cloth permits a dome design leaving, when opened, the telescope completely free without any
structure over the telescope and no massive structures besides or under it. Basis for the new design is the available prestretched
stable cloth, which is nowadays produced in much stronger qualities than used for DOT and GREGOR. The
larger curvature radius requires larger tension in the cloth, but combination with stronger cloth fits for the upscaling.
Calculations show that the steel construction geometries of the GREGOR dome can be upscaled with a few adjustments.
Bearings and drives remain within normal sizes. Cost calculations show that open-foldable domes of this size are
remarkably lower in price than closed domes. In addition, an interesting option is presented for a semi-transparent
windshield of which the position can be adapted to the wind direction. This shield gives an effective wind protection of
the region around the primary mirror without disturbing the wind flows above the shield and without stagnant air or big
eddies behind it. It is storm safe and the costs are only a fraction of the open-foldable dome costs.